In many applications, there is a desire to increase robustness and decrease cost. One application with this desire is mobile space devices, and one avenue to both, reduce costs and increase robustness, is to change the human interface portion of the mobile device, namely, by collapsing speaker and haptics functionality. To accomplish this, a piezoelectric transducer can be secured to a screen so as to vibrate the screen so as to allow the screen to function as a speaker or function as a touch screen with haptics feedback (e.g., vibratory feedback indicating a button touch).
One issue, however, is that piezoelectric transducers are generally highly capacitive loads (e.g., 1 μF), and it can be difficult to drive these transducers with sufficient quality to function as a speaker and enough power to provide a haptics effect. The best conventional technique for driving such a capacitive load employs a class G or class H boost stage with a class D amplifier. As shown in FIG. 1, this type of conventional circuit can use an average battery current of about 110 mA to drive a capacitive load of 1 μF at 10 kHz and 20Vpp with a battery voltage of about 3.6V. This particular technique, though, generally employs multiple large and expensive components (such as multiple inductors), causing this technique to be prohibitively expensive.
Therefore, there is a need for an improved driver for capacitive loads.
Another example of a conventional system is PCT Publ. No. W02009/029563.